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The AAPG/Datapages Combined Publications Database

AAPG Bulletin


Volume: 60 (1976)

Issue: 7. (July)

First Page: 1021

Last Page: 1036

Title: Sublacustrine Fan Morphology in Lake Superior

Author(s): William R. Normark (2), Franklin H. Dickson (3)


Taconite ore tailings discharged into Lake Superior off Silver Bay, Minnesota, have formed a fan-like feature 20 sq km in area with a morphology and surface-sediment distribution comparable to that of many submarine fans. Two subparallel, leveed fan valleys extend across the upper fan from the base of a virtually unchannelled delta slope. The western fan valley is the deeper of the two, and its western or right-hand (for the downstream direction) levee is higher and wider than its eastern levee, which is shared with the adjacent valley. Although both fan valleys terminate in low-relief suprafans, apparently the larger, western valley has been the primary pathway for sediments transported to the fan. The valleys give way to many small channels on the suprafans, which repre ent the only appreciable tailings deposition in the midfan area. Most of the tailings on the fan are silt-sized deposits that make up the levee complexes of the upper fan. The coarsest sediment (to coarse sand) is confined to the fan-valley floors and suprafan areas. Deposition has been insufficient to form the low half-cone physiography common to middle and lower fan segments on submarine fans. The growth pattern of Reserve fan is comparable to that of submarine fans off the California coast, primarily because of the wide range in grain size of sediment supplied (clay to coarse-pebble grade), and has developed in only 17 years owing to the very high rate of sedimentation, as much as 1.1 m/year on the upper fan.

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